JP2008258503A - Nitride-based semiconductor light emitting element, and method of fabricating nitride-based semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride-based semiconductor light emitting element having a structure in which a nonpolar nitride gallium-based semiconductor is used and which is capable of providing large luminous intensity. <P>SOLUTION: An active layer 17 is provided to generate light having a luminous wavelength of 440 nm to 550 nm. A first conductivity-type nitride gallium-based semiconductor region 13, the active layer 17, and a second conductivity-type nitride gallium-based semiconductor region 15 are disposed in a predetermined axis Ax direction. The active layer 17 includes a well layer composed of hexagonal In<SB>X</SB>Ga<SB>1-X</SB>N (0.16≤X≤0.4, X is a deformation composition), and an indium composition X is expressed with the distortion composition. An m surface of the hexagonal In<SB>X</SB>Ga<SB>1-X</SB>N faces towards the predetermined Ax axis. The well layer has a thickness of 3 nm to 20 nm. A light emitting element having a luminous wavelength of 440 nm or higher can be fabricated by making the well layer have a thickness of 3 nm or higher. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor light emitting device and a method for manufacturing a nitride semiconductor light emitting device.

  Non-Patent Document 1 describes a light emitting diode. This light emitting diode is formed on a dislocation-free m-plane of a high specific resistance GaN substrate and has a 5-period Si-doped InGaN / GaN quantum well structure. The InGaN well layer is Si-doped and has a thickness of 3 nm. The GaN barrier layer is 9 nm. The growth of the gallium nitride based semiconductor on the m-plane was performed under the growth conditions optimized for c-plane GaN. After resin sealing, with an applied current of 20 milliamps, the peak wavelength was 435 nm, the light output was 1.79 milliwatts, and the external quantum efficiency was 3.1%.

Non-Patent Document 2 describes a light emitting diode. This light emitting diode is formed on a low dislocation m-plane GaN substrate, and the carrier density of the GaN substrate is 1 × 10 ¹⁷ cm ⁻³ . This light emitting diode has a 6-cycle InGaN / GaN quantum well structure. The thickness of the InGaN well layer is 8 nm. The GaN barrier layer is 16 nm. The growth of the gallium nitride based semiconductor on the m-plane is almost the same as the growth conditions optimized for c-plane GaN. After resin sealing, with an applied current of 20 milliamps, the peak wavelength was 407 nm, the output was 23.7 milliwatts, and the external quantum efficiency was 38.9%.

Patent Document 1 describes a semiconductor laser having an In _0,1 Ga _0.9 N active layer provided on a GaN (1-100) substrate. Also described is a surface emitting semiconductor laser having an In _0.15 Ga _0.85 N well layer and an In _0.05 Ga _0.95 N barrier layer provided on a high resistivity SiC (11-20) substrate. Yes. Furthermore, a 4 nm In _0.2 Ga _0.8 N well layer and a 4 nm In _0.05 Ga _0.95 provided on a (1-100) or (11-20) high resistivity SiC substrate. A surface emitting semiconductor laser having an N barrier layer is described.
Japanese Journal of Applied Physics Vol. 45, No. 45, 2006, pp. L1197-L1199 Japanese Journal of Applied Physics Vol. 46, No.7, 2007, pp. L126-L128 (UCSB) Japanese Patent Laid-Open No. 10-135576

  Since a so-called c-plane GaN substrate is used in a semiconductor light emitting device having an active layer made of a gallium nitride based semiconductor, the influence due to the piezo effect also appears in the active layer. On the other hand, even in the case of GaN, the m-plane shows nonpolarity, and therefore, it is expected that the active layer is not affected by the piezo effect. Non-Patent Documents 1 and 2 show InGaN / GaN quantum well structure light emitting diodes fabricated on the m-plane. In Patent Document 1, although an InGaN active layer and an InGaN well layer having several indium compositions are described, there is almost no specific description regarding the emission wavelength and emission intensity.

  There is a need for a light emitting diode having an emission wavelength longer than the peak wavelength of the light emitting diodes of Non-Patent Documents 1 and 2. However, according to the inventors' experiment, when the quantum well structure is formed on the m-plane GaN using the film formation conditions for forming the quantum well structure on the c-plane GaN, a desired photoluminescence wavelength cannot be obtained. . Further, as a result of various experiments, the light emitting element of the InGaN-based active layer formed on the m-plane GaN emits light from the InGaN-based active layer formed on the c-plane GaN not only in terms of the photoluminescence wavelength but also in terms of emission intensity. It shows a tendency different from the element.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a nitride-based semiconductor light-emitting element having a structure capable of providing a favorable emission intensity while using a nonpolar gallium nitride-based semiconductor, It is another object of the present invention to provide a method for manufacturing a nitride-based semiconductor light-emitting device that uses a non-polar gallium nitride-based semiconductor and can provide good emission intensity.

According to one aspect of the present invention, a nitride semiconductor light emitting device includes (a) a first conductivity type gallium nitride semiconductor region, (b) a second conductivity type gallium nitride semiconductor region, and (c) the first conductivity type. An active layer is provided between the first-conductivity-type gallium nitride-based semiconductor region and the second-conductivity-type gallium nitride-based semiconductor region and generates light having a wavelength in the range of 440 nm to 550 nm. The active layer includes a well layer made of hexagonal In _X Ga _1-X N (0.16 ≦ X ≦ 0.4, indium composition X is a strained composition), and the thickness D of the well layer is 3 nm or more. The thickness D of the well layer is 20 nm or less, the thickness D of the indium composition X is in a relationship of X ≧ −0.16 × D + 0.88, and the first conductivity type gallium nitride based semiconductor region The active layer and the second conductivity type gallium nitride based semiconductor region are arranged in a predetermined axis direction, and the m-plane of the hexagonal In _X Ga _1-X N is in the direction of the predetermined axis. Suitable for.

According to this nitride-based semiconductor light-emitting device, since the hexagonal In _X Ga _1-X N m-plane of the well layer is oriented in the direction of a predetermined axis, the active layer exhibits substantial nonpolarity. Further, the well layer is made of hexagonal In _X Ga _1-X N (0.16 ≦ X ≦ 0.4, where X is a strain composition). The indium composition of the nonpolar InGaN well layer is larger than the indium composition of the nonpolar InGaN well layer of the nitride-based semiconductor light-emitting device formed using the c-plane deposition conditions. Therefore, the emission intensity of the nitride-based semiconductor light-emitting device of the present invention is better than that of the nitride-based semiconductor light-emitting device under the c-plane film formation conditions. Furthermore, since the well layer is made of hexagonal In _X Ga _1-X N (0.16 ≦ X ≦ 0.4, X is a strained composition), and the thickness of the well layer is greater than 3 nm and less than or equal to 20 nm, A quantum well structure is provided that generates an emission wavelength in the range of 440 nm to 550 nm.

In the nitride semiconductor light emitting device according to the present invention, the active layer may include a barrier layer made of hexagonal In _Y Ga _1-Y N (0 ≦ Y ≦ 0.05, Y is a strained composition). .

According to this nitride-based semiconductor light-emitting device, the active layer can have a quantum well structure, and the hexagonal In _Y Ga _1-Y N (0 ≦ Y ≦ 0.05, Y is a strain composition) is nonpolar. Suitable for indium composition for InGaN barrier layer.

Nitride-based semiconductor light-emitting device according to the present invention may further comprise a substrate composed of a hexagonal Al Z _Ga 1-Z _N semiconductor (0 ≦ Z ≦ 1). The first conductivity type gallium nitride based semiconductor region, the active layer, and the second conductivity type gallium nitride based semiconductor region are mounted on the main surface of the substrate.

According to this nitride semiconductor light emitting device, hexagonal Al Z _Ga 1-Z _N first conductivity type gallium nitride based semiconductor region on a semiconductor, it is possible to form the active layer and the second conductive type gallium nitride based semiconductor region These crystallinity is improved.

  In the nitride semiconductor light emitting device according to the present invention, the main surface of the substrate may be turned off from the m plane at an off angle (−2 ° ≦ θ ≦ + 2 °). According to this nitride semiconductor light emitting device, a semiconductor crystal of good quality can be obtained without being substantially affected by the polarity.

In the nitride-based semiconductor light-emitting device according to the present invention, threading dislocations in the substrate extend in the c-axis direction. According to this nitride-based semiconductor light-emitting device, threading dislocations run in the c-axis direction, so that these threading dislocations extend substantially parallel to the main surface of the substrate. In the nitride semiconductor light emitting device according to the present invention, the average density of threading dislocations across the c-plane of the substrate is preferably 1 × 10 ⁷ cm ⁻² or less. According to this nitride semiconductor light emitting device, since the density of threading dislocations across the c-plane is low, the density of threading dislocations inherited during growth on the m-plane main surface is also reduced.

  In the nitride-based semiconductor light-emitting device according to the present invention, the substrate has a first region in which threading dislocation density extending in the c-axis direction is larger than the first threading dislocation density, and threading dislocation density extending in the c-axis direction. And the second region smaller than the first threading dislocation density, and the first and second regions appear on the main surface of the substrate.

  According to this nitride semiconductor light emitting device, the semiconductor grown on the second region appearing on the m-plane main surface has a low threading dislocation density.

In the nitride-based semiconductor light-emitting device according to the present invention, the threading dislocation density in the second region is preferably less than 1 × 10 ⁷ cm ⁻² . According to this nitride-based semiconductor light-emitting device, the second region of less than 1 × 10 ⁷ cm ⁻² appears on the m-plane main surface, so that the semiconductor grown thereon has a very low threading dislocation density. .

Another aspect of the present invention is a method for fabricating a nitride-based semiconductor light-emitting device. This method, (a) preparing a substrate composed of hexagonal _{Al Z Ga 1-Z} N semiconductor (0 ≦ Z ≦ 1), (b) a first conductivity-type gallium nitride semiconductor film of the substrate (C) forming an active layer that generates light having a wavelength in the range of 440 nm to 550 nm on the first conductivity type gallium nitride semiconductor film; d) forming a second conductivity type gallium nitride based semiconductor film on the active layer. The first conductive type gallium nitride based semiconductor film, the active layer, and the second conductive type gallium nitride based semiconductor film are arranged in a direction of a predetermined axis on the main surface of the substrate to form the active layer In the step, the first semiconductor layer made of hexagonal In _X Ga _1-X N (0.16 ≦ X ≦ 0.4, X is a strained composition) and having the first gallium composition is formed at the first temperature. growing, in the step of forming the active layer, hexagonal _{in Y Ga 1-Y N (} 0 ≦ Y ≦ 0.05, Y <X, Y : strained composition) of the second gallium composition made from the Two semiconductor layers are grown at a second temperature, the first gallium composition is lower than the second gallium composition, the first temperature is lower than the second temperature, and the first temperature the difference between the second temperature is less than 95 degrees with the hexagonal _{an in} X Ga ₁ M surface of _{X N} is oriented in the direction of the predetermined axis.

According to this method, the first gallium composition is lower than the second gallium composition in the production of an active layer in which the m-plane of hexagonal In _X Ga _1-X N faces the predetermined axis. Since the difference in growth temperature between the two types of gallium nitride semiconductors is 95 degrees or more, the indium composition of the first semiconductor layer can be increased and applied as a well layer.

In the method according to the present invention, the substrate is cut out so as to intersect the crystal in the c-axis direction in the grown hexagonal Al Z _Ga 1-Z _N semiconductor (0 ≦ Z ≦ 1) in the m-axis The main surface of the substrate is polished and extends along a plane that intersects the m-axis.

In this method, since crystal growth proceeds in the c-axis direction, threading dislocations also extend in the c-axis direction. If cut out of a hexagonal _{Al Z Ga 1-Z} N semiconductor crystal so as to intersect the semiconductor plate in the m-axis, the active layer m-plane of the hexagonal _{In X Ga 1-X} N is oriented in the direction of the predetermined axis A suitable substrate is provided for fabricating the substrate.

  In the method according to the present invention, the substrate has a plurality of first regions in which the density of threading dislocations extending in the c-axis direction is higher than the first threading dislocation density, and the density of threading dislocations extending in the c-axis direction is the first. A plurality of second regions smaller than the threading dislocation density, wherein the first and second regions are alternately arranged, and the first and second regions appear on the main surface of the substrate. Can be.

  According to this method, the semiconductor grown on the second region appearing on the m-plane main surface has a low threading dislocation density.

In the method according to the present invention, the threading dislocation density in the second region is preferably less than 1 × 10 ⁷ cm ⁻² . According to this method, a semiconductor crystal of good quality can be obtained without being affected by dislocations.

  In the method according to the present invention, the main surface of the substrate may be turned off at an off angle (−2 ° ≦ θ ≦ + 2 °) from the m-plane. According to this method, a semiconductor crystal of good quality can be obtained without being substantially affected by polarity.

  The method according to the present invention may further include a step of heat-treating the substrate while supplying a gas containing ammonia and hydrogen prior to the formation of the first conductivity type gallium nitride based semiconductor film.

  In this method, since the substrate is heat-treated in a gas containing ammonia and hydrogen before the growth of the gallium nitride-based semiconductor, a flat substrate surface can be easily obtained, and a semiconductor light-emitting element having better light emission characteristics can be obtained.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, there is provided a nitride-based semiconductor light-emitting device having a structure that uses a non-polar gallium nitride-based semiconductor and can provide good light emission intensity. In addition, according to the present invention, a method for producing a nitride-based semiconductor light-emitting element can be provided, and according to this method, a non-polar gallium nitride-based semiconductor can be used and good emission intensity can be provided.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments of the nitride-based semiconductor light-emitting device and the method for manufacturing the nitride-based semiconductor light-emitting device of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

FIG. 1 is a drawing schematically showing a nitride-based semiconductor light-emitting device according to this embodiment. Examples of the nitride semiconductor light emitting device include a light emitting diode and a semiconductor laser. The nitride semiconductor light emitting device 11 includes a first conductivity type gallium nitride semiconductor region 13, a second conductivity type gallium nitride semiconductor region 15, and an active layer 17. The active layer 17 is provided between the first conductivity type gallium nitride semiconductor region 13 and the second conductivity type gallium nitride semiconductor region 15. The active layer 17 can consist of a single InGaN semiconductor well layer or can have a quantum well structure 19. The active layer 17 is provided so as to generate light having a wavelength of 440 nm or more. The active layer 17 is provided to generate light having a wavelength in the range of 550 nm or less. The first conductivity type gallium nitride based semiconductor region 13, the active layer 17, and the second conductivity type gallium nitride based semiconductor region 15 are arranged in the direction of a predetermined axis Ax. The active layer 17 includes a well layer made of hexagonal In _X Ga _1-X N, and the indium composition X is represented by a strain composition. The m-plane of hexagonal In _X Ga _1-X N faces the direction of a predetermined axis Ax. Carriers provided from the first conductivity type gallium nitride semiconductor region 13 and the second conductivity type gallium nitride semiconductor region 15 are confined in the well layer of the active layer 17. Compared to the band gap of the well layer, the band gaps of the first conductivity type gallium nitride semiconductor region 13 and the second conductivity type gallium nitride semiconductor region 15 are large.

  By setting the thickness of the well layer to 3 nm or more, a light-emitting element having an emission wavelength of 440 nm or more can be manufactured. If the thickness of the well layer exceeds 20 nm, the crystal quality of InGaN deteriorates and the light emission characteristics deteriorate.

As understood from the coordinate system shown in FIG. 1, hexagonal In _X Ga _1-X N is expressed using the c axis and three axes a 1, a 2, and a 3 orthogonal to the c axis. The three axes a1, a2, and a3 form an angle of 120 degrees (γ ₁ , γ ₂ , γ ₃ ). The hexagonal c-axis is directed to the Z-axis of the orthogonal coordinate system S, and the axis a2 is directed to the X-axis of the orthogonal coordinate system S. FIG. 1 shows a typical m-plane.

In the nitride-based semiconductor light-emitting element 11 in which the m-plane of this hexagonal In _X Ga _1-X N faces the direction of the predetermined axis Ax, if the indium composition X is 0.16 or more, the emission wavelength is 440 nm or more. It is suitable as an active layer for a light emitting device. On the other hand, when the indium composition X exceeds 0.4, the crystal quality of InGaN deteriorates and the light emission characteristics deteriorate.

  The reason for this is as follows. Even if the indium composition of the InGaN-based light-emitting element formed on the m-plane GaN is the same as the indium composition of the InGaN-based light-emitting element formed on the c-plane GaN, the photo of the InGaN-based light-emitting element formed on the m-plane GaN The luminescence wavelength is shorter than the photoluminescence wavelength of the InGaN-based light emitting device formed on the c-plane GaN. For this reason, in order to obtain a desired photoluminescence wavelength in an InGaN-based light emitting element formed on m-plane GaN, InGaN having a larger indium composition must be grown. Further, in order to increase the wavelength of light emitted from the light emitting diodes of Non-Patent Documents 1 and 2, it is necessary to further increase the indium composition.

As described above, according to the nitride-based semiconductor light-emitting element 11, the hexagonal In _X Ga _1-X N m-plane of the well layer is oriented in the direction of the predetermined axis. Indicates polarity. The well layer of the active layer 17 is made of hexagonal In _X Ga _1-X N (0.16 ≦ X ≦ 0.4, where X is a strained composition). Since the indium composition of the nonpolar InGaN well layer was set to a value larger than the indium composition of the nonpolar InGaN well layer of the nitride-based semiconductor light-emitting device formed using the c-plane deposition conditions, the c-plane Compared with the nitride-based semiconductor light-emitting device according to the film forming conditions for use, the emission intensity of the nitride-based semiconductor light-emitting device of the present case is improved. Furthermore, the well layer is hexagonal _{In X Ga 1-X N (} 0.16 ≦ X ≦ 0.4, X : strained composition) of the active layer 17 with made of, the thickness of the well layer is greater 20nm or less than 3nm Therefore, the active layer 17 is provided so as to generate light having a light emission wavelength in the range of 440 nm to 550 nm.

  The first conductivity type gallium nitride semiconductor region 13 can include, for example, a clad layer 21 made of a gallium nitride semiconductor having a band gap larger than that of the active layer. The gallium nitride semiconductor is, for example, n-type GaN. is there. If necessary, the first conductivity type gallium nitride based semiconductor region 13 may include a semiconductor layer 23 made of an n-type AlGaN gallium nitride semiconductor.

  The second conductivity type gallium nitride based semiconductor region 15 can include, for example, an electron block layer 25 made of a gallium nitride based semiconductor having a band gap larger than the band gap of the active layer, and the gallium nitride based semiconductor is, for example, p-type AlGaN It is. The second conductivity type gallium nitride based semiconductor region 15 can include a contact layer 27 made of, for example, a p-type gallium nitride based semiconductor, and the gallium nitride based semiconductor is, for example, p-type GaN.

In the nitride semiconductor light emitting device 11 of one embodiment, the active layer 17 can include a quantum well structure 19. The quantum well structure 19 can include a well layer 29a and a barrier layer 29b. The well layers 29a and the barrier layers 29b are alternately arranged. In the nitride-based semiconductor light-emitting element 11, the well layer 29 a can be made of hexagonal In _X Ga _1-X N (0.16 ≦ X ≦ 0.4, where X is a strain composition). Further, the barrier layer 29b of the active layer 17, the hexagonal _{In Y Ga 1-Y N (} 0 ≦ Y ≦ 0.05, Y : strained composition) can be made of. Hexagonal In _Y Ga _1-Y N is suitable for the indium composition for the nonpolar InGaN barrier layer. The indium composition of the hexagonal In _Y Ga ₁ -YN may be 0 or more. Further, the gallium composition of the hexagonal In _Y Ga _1-Y N may be 0.05 or less. This is because a sufficient energy barrier is obtained between the well layer. This gallium composition is represented by a strain composition. The thickness of the barrier layer 29b can be 5 nm or more. This is because carriers can be sufficiently confined in the well layer. The film thickness of the barrier layer 29b can be 20 nm or less. This is because a sufficiently low element resistance can be obtained. The barrier layer 29b is made of, for example, GaN or InGaN.

Nitride semiconductor light emitting device 11 may further include a substrate 31 composed of hexagonal _{Al Z Ga 1-Z} N semiconductor (0 ≦ Z ≦ 1). The substrate 31 preferably exhibits conductivity. The first conductivity type gallium nitride based semiconductor region 13, the active layer 17 and the second conductivity type gallium nitride based semiconductor region 15 are mounted on the main surface 31 a of the substrate 31. Hexagonal Al Z _Ga 1-Z _N semiconductor first conductivity type gallium nitride based on the semiconductor region 13, it is possible to form the active layer 17 and the second conductive type gallium nitride based semiconductor region 15, these crystallinity satisfactorily Become. As the material of the substrate 31, for example, GaN, AlGaN, AlN, or the like can be used. Preferably, the material of the substrate 31 is n-type GaN. An electrode 32 a (for example, a cathode) is provided on the back surface 31 b of the substrate 31, and another electrode 32 b (for example, an anode) is provided on the contact layer 27.

The main surface 31a of the substrate 31 can be parallel to the m-plane, but can be off at a certain off-angle from the m-plane. The off angle Angle _OFF is defined by an angle formed by the normal line of the main surface 31a of the substrate 31 and the normal line of the m-plane. The off angle Angle _OFF can be, for example, an angular range of −2 ° ≦ θ ≦ + 2 ° in the c-axis direction, and an angular range of −2 ° ≦ θ ≦ + 2 ° in the a-axis direction. According to this substrate 31, a semiconductor crystal of good quality can be obtained without being affected by polarity.

In the nitride semiconductor light emitting device 11, threading dislocations in the substrate 31 extend in the c-axis direction. Since threading dislocations run in the c-axis direction, these threading dislocations extend substantially parallel to the main surface 31a of the substrate 31. The average density of threading dislocations across the c-plane of the substrate 31 is preferably 1 × 10 ⁷ cm ⁻² (for example, the density of threading dislocations randomly distributed) or less. According to this substrate 31, since the density of threading dislocations across the c-plane is low, the density of threading dislocations inherited during growth on the m-plane main surface is also reduced. Such a substrate 31 is cut out so as to intersect the crystal in the c-axis direction in the grown hexagonal _{Al Z Ga 1-Z} N semiconductor (0 ≦ Z ≦ 1) in the m-axis, the principal surface 31a Extends along a plane that is polished and intersects the m-axis. Since the growth of the semiconductor crystal for the substrate 31 proceeds in the c-axis direction, threading dislocations also extend in the c-axis direction. If cut out of a hexagonal _{Al Z Ga 1-Z} N semiconductor crystal so as to intersect the semiconductor plate in the m-axis, this substrate 31 is, m-plane of the hexagonal _{In X Ga 1-X} N is a predetermined axis Ax Suitable for producing an active layer oriented in the direction.

  FIG. 2 is a drawing showing an example of a gallium nitride substrate for the nitride-based semiconductor light-emitting element 11. FIG. 2 also shows a coordinate system for the hexagonal system as in FIG. In FIG. 2, the c-plane is indicated by the reference symbol “C”, and the m-plane is indicated by the reference symbol “M”. The first surface 33a of the example gallium nitride substrate 33 includes a first area where a first region (high dislocation region) 33c having a relatively high threading dislocation density appears and a first area having a relatively small threading dislocation density. 2 region (low dislocation region) 33d appears. The first regions 33c and the second regions 33d are alternately arranged, and the first area has a stripe shape on the first surface 33a. Most of threading dislocations run in the c-axis direction. A semiconductor grown on the second region 33d appearing on the m-plane main surface has a low threading dislocation density. As already described, the first surface 33a of the gallium nitride substrate 33 can be inclined at an angle with respect to the m-plane.

The threading dislocation density of the second region 33d in the c-plane is preferably 1 × 10 ⁷ cm ⁻² or less, for example. Since the second region 33d of 1 × 10 ⁷ cm ⁻² or less appears on the m-plane main surface, the semiconductor grown on the second region 33d has a very low threading dislocation density.

FIG. 3 is a drawing showing another example of a gallium nitride substrate for the nitride-based semiconductor light-emitting element 11. FIG. 3 also shows a coordinate system for the hexagonal system as in FIG. In FIG. 3, the c-plane is indicated by the reference symbol “C”, and the m-plane is indicated by the reference symbol “M”. The first surface 35a of the example gallium nitride substrate 35 includes a first area where a first region (high dislocation region) 35c having a relatively high threading dislocation density appears and a first area having a relatively small threading dislocation density. 2 region (low dislocation region) 35d appears. The first area 35c is arranged in the second area 35d. For this reason, on the first surface 35a, the first area is arranged in a dot shape within the second area. Many threading dislocations run in the c-axis direction. A semiconductor grown on the second region 35d appearing on the m-plane principal surface has a low threading dislocation density. As already described, the first surface 35a of the gallium nitride substrate 35 can be inclined at an angle with respect to the m-plane. The threading dislocation density of the second region 35d on the c-plane is preferably 1 × 10 ⁷ cm ⁻² or less, for example. A substrate in which only the second region (low dislocation region) 35d appears on the first surface 35a by cutting the m-plane so that the first region (high dislocation region) 35c does not appear on the first surface 35a. Can be produced. Since the second region 35d of 1 × 10 ⁷ cm ⁻² or less appears on the m-plane main surface, the semiconductor grown on the second region 35d has a very low threading dislocation density.

(Example)
As described below, a light-emitting element including an active layer provided to generate light having a wavelength in a range of 440 nm to 550 nm can be manufactured. In this example, a blue light emitting device was fabricated by metal organic vapor phase epitaxy. Trimethylgallium, trimethylaluminum, trimethylindium, ammonia, monosilane, and cyclopentadienylmagnesium were used as raw materials for the metal organic chemical vapor deposition method. FIG. 4 is a drawing showing a flow 100 of main steps for manufacturing a light-emitting element.

As shown in FIG. 4, in step S101, preparing a substrate composed of hexagonal _{Al Z Ga 1-Z} N semiconductor (0 ≦ Z ≦ 1). In this example, an n-type GaN crystal having a low defect region with a threading dislocation density of less than 1 × 10 ⁶ cm ^{−2 on} the c-plane and a defect concentration region distributed in a stripe shape is grown in the (0001) direction. Then, after forming the GaN self-solid, the GaN self-solid was polished to prepare an m-plane GaN (10-10) substrate.

  In step S103, prior to the formation of the first conductivity type gallium nitride based semiconductor film, the m-plane GaN substrate is heat-treated while supplying a gas containing ammonia and hydrogen. For this purpose, an n-type m-plane GaN substrate is placed on the susceptor, the furnace pressure is controlled to 30 kPa, ammonia and hydrogen are supplied into the furnace, and cleaning is performed for 10 minutes at a substrate temperature of 1050 degrees Celsius. It was. By this heat treatment, a flat substrate surface can be easily obtained, and a semiconductor light emitting device having better light emission characteristics can be obtained.

In step S105, a first conductivity type gallium nitride based semiconductor film is then formed on the main surface of the substrate. In this example, after raising the substrate temperature to 1100 degrees Celsius, an n-type Al _0.12 Ga _0.88 N layer was grown. For this growth, trimethylgallium (24 μmol / min), trimethylaluminum (4.3 μmol / min), ammonia (0.22 mol / min), and monosilane were supplied mainly using hydrogen as a carrier gas. The AlGaN film thickness is 50 nm, for example.

  Next, the growth was interrupted once, the substrate temperature was raised to 1150 degrees Celsius, and then an n-type GaN layer was grown. For this growth, trimethylgallium (244 μmol / min), ammonia (0.33 mol / min), and monosilane were supplied mainly using hydrogen as a carrier gas. The film thickness of the GaN film is 2 μm, for example.

Next, in step S107, an active layer that generates light having a wavelength in the range of 440 nm to 550 nm is formed on the first conductivity type gallium nitride semiconductor film. For this purpose, the growth was temporarily interrupted, the substrate temperature was lowered to 880 degrees Celsius, and then an In _0.01 Ga _0.99 N barrier layer was grown. The thickness of this barrier layer is 15 nm, for example. For this growth, trimethylgallium (24 μmol / min), trimethylindium (1.6 μmol / min), and ammonia (0.27 mol / min) were supplied mainly using nitrogen as a carrier gas. After growing the InGaN barrier layer, the substrate temperature was lowered to 780 degrees Celsius, and then an In _0.27 Ga _0.73 N well layer was grown. The thickness of this well layer is 4 nm, for example. For this growth, trimethylgallium (24 μmol / min), trimethylindium (24 μmol / min), ammonia (0.36 mol / min) were supplied mainly using nitrogen as a carrier gas. By repeating the growth of the undoped barrier layer and the undoped well layer, for example, a six-period quantum well layer was formed.

Next, in step S109, a second conductivity type gallium nitride based semiconductor film is formed on the active layer. For this purpose, the growth was interrupted again, the substrate temperature was raised to 1050 degrees Celsius, and then a p-type Al _0.15 Ga _0.85 N electron blocking layer was grown. For this growth, trimethylgallium (24 μmol / min), trimethylaluminum (2.3 μmol / min), ammonia (0.22 mol / min), and cyclopentadienylmagnesium were supplied mainly using hydrogen as a carrier gas. The thickness of the electron block layer is, for example, 20 nm.

  After growing the p-type AlGaN electron block layer, a p-type GaN layer was grown. For this growth, trimethylgallium (99 μmol / min), ammonia (0.22 mol / min), and cyclopentadienylmagnesium were supplied mainly using hydrogen as a carrier gas. The thickness of this GaN layer is, for example, 25 nm.

  After growing the p-type GaN layer, a p-type GaN contact layer was grown. The thickness of the p-type GaN contact layer is, for example, 25 nm. For this growth, trimethylgallium (67 μmol / min), ammonia (0.22 mol / min), and cyclopentadienylmagnesium were supplied mainly using hydrogen as a carrier gas. Through these steps, an epitaxial substrate for the light emitting diode (LED) was produced. The m-plane of each gallium nitride based semiconductor film of the epitaxial substrate is substantially parallel to a plane extending along the main surface of the GaN substrate.

Thereafter, the GaN substrate was taken out from the furnace, and X-ray diffraction measurement (ω-2θ measurement) of the (1-100) plane was performed. FIG. 5A is a drawing showing the measurement result of the X-ray angle distribution. According to this measurement, the In composition of the InGaN well layer was about 27%. A 400 μm square (electrode area, for example, 1.6 × 10 ⁻³ cm ² ) translucent p-electrode is formed on the p-type GaN layer of the epitaxial substrate with an appropriate metal material, and an n-electrode is formed on the back surface of the GaN substrate. Formed. As a result, an LED element was produced.

FIG. 6 shows an emission spectrum obtained by applying a pulse current to the bare-chip LED at room temperature. FIG. 7 is a diagram showing current-light output characteristics and current-external quantum efficiency characteristics. The peak emission wavelength is 462 nm, which is pure blue. At a current value of 20 mA (current density: 12.5 A / cm ² ), the light output was 1.4 mW and the external quantum efficiency was 2.6%. At a current value of 200 mA (current density 125 A / cm ² ), the light output was 13.2 mW and the external quantum efficiency was 2.4%. This chip was molded with an epoxy resin to produce an LED lamp. In the measurement after mold sealing, at a current value of 20 mA (current density 12.5 A / cm ² ), the peak wavelength was 462 nm, the light output was 4.2 mW, and the external quantum efficiency was 7.8%.

In this LED, the first conductivity type gallium nitride semiconductor film, the active layer, and the second conductivity type gallium nitride semiconductor film are mounted on the main surface of the GaN substrate, and are sequentially arranged in the direction of a predetermined axis. ing. Hexagonal _{In X Ga 1-X N (} 0.16 ≦ X ≦ 0.4, X : strained composition) as well as growth of the semiconductor layer for the well of the first gallium fraction consists in a first temperature _{T W} , hexagonal _{in Y Ga 1-Y N (} 0 ≦ Y ≦ 0.05, Y <X, Y : strained composition) a semiconductor layer for barrier second gallium composition consists at a second temperature _{T B} grown. The first gallium composition is lower than the second gallium composition, the first temperature T _W is the difference between the second lower than the temperature T _B, the first temperature T _W and the second temperature T _B 95 More than degrees. According to this method, the first gallium composition is lower than the second gallium composition in the production of an active layer in which the m-plane of hexagonal In _X Ga _1-X N faces the predetermined axis. Since the difference in growth temperature between the two types of gallium nitride based semiconductors is 95 degrees or more, the indium composition of the first semiconductor layer can be increased and applied as a well layer.

FIG. 8 is a drawing showing the relationship between the indium composition and the thickness of the well layer for the active layer provided to generate light having a wavelength in the range of 440 nm to 550 nm. The active layer in the region “A1” can generate light having a wavelength in the range of 440 nm to 550 nm. In the region “A2”, the indium composition is too low and the active layer cannot generate light having a wavelength of 440 nm or more. In the region “A3”, the well layer is too thin and the active layer cannot generate light having a wavelength of 440 nm or more. In the region “A4”, the active layer cannot generate light having a wavelength of 440 nm or more because of the relationship between the indium composition and the well layer thickness. In the region “A5”, the indium composition is too high to obtain a high-quality InGaN crystal. In FIG. 8, line L1: X = 0.4
Line L2: X = 0.16
Line L3: D = 3
Line L4: X = −0.16 × D + 0.88
Line L5: D = 20
And points P _{1 to} P ₅ indicate measurement points at emission wavelengths of 395 nm, 420 nm, 460 nm, 474 nm, and 477 nm, respectively. Regarding the relationship between the indium composition and the thickness of the well layer for the active layer provided so that the region (including the boundary) surrounded by the lines L1 to L5 generates light having a wavelength in the range of 440 nm to 550 nm. Is preferred.

  As can be seen from FIG. 8, increasing indium is not easy. An InGaN well layer was grown at a substrate temperature of 750 degrees Celsius, and the other conditions were the same as in Example 1 to produce an LED epitaxial substrate. The appearance of this epitaxial substrate was blackened, and no photoluminescence spectrum from the quantum well light emitting layer was observed. FIG. 5B is a drawing showing the results of X-ray diffraction measurement (ω-2θ measurement) of the (10-10) plane of this epitaxial substrate. No satellite peak is observed in the quantum well light emitting layer. Therefore, the quantum well structure is not formed. The indium composition is estimated to exceed 40%. Thus, when the indium composition is increased in the growth of InGaN, the crystal quality is extremely deteriorated.

  Further, the growth of the InGaN well layer was set to 58 μmol / min for the supply amount of trimethylindium, and the other conditions were the same as in Example 1 to produce an LED epitaxial substrate. The appearance of this epitaxial substrate was blackened, and no photoluminescence spectrum from the quantum well light emitting layer was observed. In the result of X-ray diffraction measurement (ω-2θ measurement) on the (10-10) plane, no satellite peak of the quantum well light emitting layer was observed. Therefore, the quantum well structure is not formed. The indium composition is estimated to exceed 40%. From these facts, it is understood that the crystal quality becomes extremely worse when the InGaN composition is increased.

  Therefore, in order to fabricate a light emitting device using the m-plane, it is important to control the thickness of the well layer and the indium composition of the well layer, and to increase the growth temperature difference between the well layer and the barrier layer. .

Yet another embodiment will be described. Using the same growth conditions as in Example 1, the thickness of the InGaN well layer was changed to 3 nm, 4 nm, and 5 nm to produce an epitaxial substrate with an LED structure. FIG. 9 shows the relationship between the thickness of the well layer and the PL spectra W ₃ , W ₄ , and W ₅ . As the well layer becomes thicker, the PL wavelength becomes longer. Referring to FIG. 9, the PL wavelength is 460 nm when the well width is 4 nm, and the PL wavelength is 475 nm when the well width is 5 nm.

When an LED was fabricated using an epitaxial substrate in the same manner as in Example 1, high light output and external quantum efficiency were obtained as in Example 1. For example, the peak emission wavelength is 470 nm, which is pure blue. At a current value of 20 mA (current density: 12.5 A / cm 2), the light output was 1.6 mW and the external quantum efficiency was 3.0%. At a current value of 200 mA (current density 125 A / cm ² ), the light output was 13.7 mW and the external quantum efficiency was 2.6%. This chip was molded with an epoxy resin to produce an LED lamp. In the measurement after mold sealing, at a current value of 20 mA (current density 12.5 A / cm 2), the peak wavelength was 470 nm, the light output was 4.8 mW, and the external quantum efficiency was 9.0%.

An LED was fabricated using a substrate different from the GaN substrate.
Using the same conditions as in Example 1, an epitaxial structure for LED was grown on a 4H—SiC (10-10) substrate or a LiAlO ₂ (100) substrate instead of an n-type m-plane GaN (10-10) substrate. LED was produced. Many stacking faults occurred, and only a very weak output was obtained.

Moreover, LED was produced using the c-plane GaN substrate. A blue light emitting device was fabricated by metal organic vapor phase epitaxy as follows. Trimethylgallium, trimethylaluminum, trimethylindium, ammonia, monosilane, and cyclopentadienylmagnesium were used as raw materials. The c-plane GaN substrate was fabricated by slicing and polishing n-type GaN grown in the (0001) direction having a low defect region with a threading dislocation density of less than 1 × 10 ⁶ cm ⁻² and a defect concentration region distributed linearly. .

  An n-type c-plane GaN (0001) substrate was placed on the susceptor, ammonia and hydrogen were introduced into the furnace while controlling the furnace pressure to 30 kPa, and cleaning was performed at a substrate temperature of 1050 degrees Celsius for 10 minutes. After raising the substrate temperature to 1100 ° C., trimethylgallium (24 μmol / min), trimethylaluminum (4.3 μmol / min), ammonia (0.22 mol / min), and monosilane were introduced mainly using hydrogen as a carrier gas. Then, an n-type AlGaN layer (Al composition 12%) having a thickness of 50 nm was grown. Next, after the growth is temporarily interrupted and the substrate temperature is raised to 1150 degrees Celsius, trimethylgallium (244 μmol / min), ammonia (0.33 mol / min), monosilane are introduced mainly using hydrogen as a carrier gas, An n-type GaN layer having a thickness of 2 μm was grown.

  Next, the growth was temporarily interrupted, and the substrate temperature was lowered to 880 degrees Celsius. Then, trimethylgallium (24 μmol / min), trimethylindium (1.6 μmol / min), ammonia (0. 27 mol / min) and an InGaN barrier layer (In composition 1%) having a thickness of 15 nm is grown, the substrate temperature is lowered to 800 degrees Celsius, and the carrier gas is mainly nitrogen and trimethylgallium (16 μmol / min) Then, trimethylindium (13 μmol / min) and ammonia (0.36 mol / min) were introduced to grow an InGaN well layer having a thickness of 3 nm. By repeating this process, a 6-cycle quantum well light-emitting layer was formed.

  Next, after the growth was interrupted again and the substrate temperature was raised to 1050 degrees Celsius, trimethylgallium (17 μmol / min), trimethylaluminum (2.8 μmol / min), ammonia (0. 22 mol / min), cyclopentadienyl magnesium was introduced, and a 20 nm-thick p-type AlGaN electron blocking layer (Al composition 18%) was grown. Thereafter, trimethylgallium (99 μmol / min), ammonia (0.22 mol / min), and cyclopentadienylmagnesium were introduced mainly using hydrogen as a carrier gas, and a p-type GaN layer having a thickness of 25 nm was grown. Next, trimethylgallium (67 μmol / min), ammonia (0.22 mol / min), and cyclopentadienylmagnesium were introduced mainly using hydrogen as a carrier gas, and a p-type GaN contact layer having a thickness of 25 nm was grown.

Thereafter, when the GaN substrate was taken out of the furnace and subjected to X-ray diffraction measurement (ω-2θ measurement), the In composition of the InGaN well layer was about 10%. In this LED epi structure, a 400 μm square (electrode area 1.6 × 10 ⁻³ cm ² ) translucent p electrode is formed on a p-type GaN layer with an appropriate metal material, and an n electrode is formed on the back surface of the GaN substrate. An element was produced. When a pulse current was applied to the bare chip LED at room temperature, a high emission efficiency was obtained with pure blue having a wavelength of 460 nm, but as shown in FIG. 10, a blue shift of the emission wavelength accompanying an increase in current was observed. . On the other hand, in the LED of Example 1, the blue shift of the emission wavelength accompanying the increase in current was not observed.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1 is a drawing schematically showing a nitride-based semiconductor light-emitting device according to this embodiment. FIG. 2 is a drawing showing an example of a gallium nitride substrate for a nitride-based semiconductor light emitting device. FIG. 3 is a drawing showing another example of a gallium nitride substrate for a nitride semiconductor light emitting device. FIG. 4 is a drawing showing main steps for manufacturing a light-emitting element. FIG. 5 is a drawing showing the results of X-ray diffraction measurement (ω-2θ measurement) on the (10-10) plane. FIG. 6 is a graph showing an emission spectrum obtained by applying a pulse current to a bare-chip LED at room temperature. FIG. 7 is a diagram showing current-light output characteristics and current-external quantum efficiency characteristics. FIG. 8 is a drawing showing the relationship between the indium composition and the thickness of the well layer for the active layer provided to generate light having a wavelength in the range of 440 nm to 550 nm. FIG. 9 is a drawing showing the relationship between the thickness of the well layer and the PL wavelength. FIG. 10 is a drawing showing a blue shift of the emission wavelength accompanying an increase in current in an LED fabricated on a c-plane substrate.

Explanation of symbols

Ax ... predetermined axis, 11 ... nitride semiconductor light emitting device, 13 ... first conductivity type gallium nitride semiconductor region, 15 ... second conductivity type gallium nitride semiconductor region, 17 ... active layer, 19 ... quantum well structure, DESCRIPTION OF SYMBOLS 21 ... Cladding layer, 23 ... Semiconductor layer, 25 ... Electron block layer, 27 ... Contact layer, 29a ... Well layer, 29b ... Barrier layer, 31 ... Substrate, 32a, 32b ... Electrode, 33, 35 ... Substrate, 33c, 35c ... First region (high dislocation region), 33d, 35d ... Second region (low dislocation region)

Claims (13)

A first conductivity type gallium nitride based semiconductor region;
A second conductivity type gallium nitride based semiconductor region;
An activity provided between the first conductive type gallium nitride based semiconductor region and the second conductive type gallium nitride based semiconductor region and configured to generate light having a wavelength in the range of 440 nm to 550 nm. With layers,
The active layer includes a well layer made of hexagonal In _X Ga _1-X N (0.16 ≦ X ≦ 0.4, indium composition X is a strained composition),
The thickness D of the well layer is greater than 3 nm;
The well layer has a thickness D of 20 nm or less,
The thickness D of the indium composition X has a relationship of X ≧ −0.16 × D + 0.88,
The first conductivity type gallium nitride based semiconductor region, the active layer and the second conductivity type gallium nitride based semiconductor region are arranged in a predetermined axis direction,
A nitride-based semiconductor light-emitting element, wherein an m-plane of the hexagonal In _X Ga _1-X N faces the direction of the predetermined axis. The active layer, hexagonal _{In Y Ga 1-Y N (} 0 ≦ Y ≦ 0.05, Y : strained composition) nitride according to claim 1 including a barrier layer made of, it is characterized by -Based semiconductor light emitting device. Further comprising a substrate made of a hexagonal _{Al Z Ga 1-Z} N semiconductor (0 ≦ Z ≦ 1),
The first conductivity type gallium nitride based semiconductor region, the active layer, and the second conductivity type gallium nitride based semiconductor region are mounted on a main surface of the substrate. 2. The nitride-based semiconductor light-emitting device described in 2.   4. The nitride-based semiconductor light-emitting element according to claim 3, wherein the main surface of the substrate is turned off at an off angle (−2 ° ≦ θ ≦ + 2 °) from the m-plane. The threading dislocation of the substrate extends in the c-axis direction,
5. The nitride-based semiconductor light-emitting element according to claim 3, wherein the density of threading dislocations across the c-plane of the substrate is 1 × 10 ⁷ cm ⁻² or less. The substrate includes a first region in which threading dislocation density extending in the c-axis direction is higher than the first threading dislocation density, and a second region in which threading dislocation density extending in the c-axis direction is smaller than the first threading dislocation density. Including
The nitride-based semiconductor light-emitting element according to claim 3 or 4, wherein the first and second regions appear on the main surface of the substrate. The nitride-based semiconductor light-emitting element according to claim 6, wherein a density of the threading dislocations in the second region is less than 1 × 10 ⁷ cm ⁻² . A method for producing a nitride-based semiconductor light-emitting device, comprising:
Preparing a substrate made of a hexagonal Al _Z Ga _1-Z N semiconductor (0 ≦ Z ≦ 1);
Forming a first conductivity type gallium nitride based semiconductor film on the main surface of the substrate;
Forming an active layer on the first conductivity type gallium nitride based semiconductor film to generate light having a wavelength in the range of 440 nm to 550 nm;
Forming a second conductivity type gallium nitride based semiconductor film on the active layer,
The first conductive type gallium nitride based semiconductor film, the active layer, and the second conductive type gallium nitride based semiconductor film are arranged in a predetermined axis direction on the main surface of the substrate,
In the step of forming the active layer, a first semiconductor layer made of hexagonal In _X Ga _1-X N (0.16 ≦ X ≦ 0.4, X is a strain composition) and having a first gallium composition is formed. Grow at a first temperature,
In the step of forming the active layer, hexagonal _{In Y Ga 1-Y N (} 0 ≦ Y ≦ 0.05, Y <X, Y : strained composition) a second semiconductor of the second gallium fraction consists Growing the layer at a second temperature;
The first gallium composition is lower than the second gallium composition;
The first temperature is lower than the second temperature;
The difference between the first temperature and the second temperature is 95 degrees or more,
The m-plane of the hexagonal In _X Ga _1-X N faces the direction of the predetermined axis. The substrate is cut out so as to intersect the crystal in the c-axis direction in the grown hexagonal Al Z _Ga 1-Z _N semiconductor (0 ≦ Z ≦ 1) in the m-axis, the main surface of the substrate 9. The method of claim 8, wherein the method is polished and extends along a plane that intersects the m-axis. The substrate includes a plurality of first regions in which threading dislocation density extending in the c-axis direction is larger than the first threading dislocation density, and a plurality of threading dislocation densities extending in the c-axis direction are smaller than the first threading dislocation density. A second region,
The first and second regions are arranged alternately,
10. The method according to claim 8, wherein the first and second regions appear on the main surface of the substrate. The method of claim 10, wherein the threading dislocation density in the second region is less than 1 × 10 ⁷ cm ⁻² .   The main surface of the substrate is off from the m-plane at an off angle (-2 ° ≦ θ ≦ + 2 °). Method. 13. The method according to claim 8, further comprising a step of heat-treating the substrate while supplying a gas containing ammonia and hydrogen prior to the formation of the first conductivity type gallium nitride based semiconductor film. The method described in any one of the paragraphs.

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